Amplifier circuits



J. W. FOLEY AMPLIFIER CIRCUITS Jan. 3, 1928.

lled Dec 15, 1923 remote from the substations.

Patented Jan. 3, 1928.

UNITED STATES PATENT OFFICE.

JOHN W. FOLEY, OF IBOGOTA, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

AMPLIFIER CIRCUITS.

Application filed December 1 This invention relates to telephony, and aims to provide for faithfully and efficiently reproducing sound waves as electric current variations and faithfully and efficiently amplifying the current variations before transmitting them from a subscribers station or substation over the line.

In the forms of the invention specifically shown and described herein for purposes of illustration, the amplifying means is supplied with direct current from the central station over the same conductor line used to transmit talking currents, and the output circuit of the amplifying device is connected to the line through a transformer so that the amplification may be faithful and efficient in spite of whatever difference there may be between the impedances facing the transformer.

The means for converting the sound waves into electric currents may also be supplied with direct current over the line used to transmit the talkin currents. Thus, the transmitter may be a type having high modulating efficiency. If desired, the transmitter may be of the balanced type, to facilitate accuracy in the reproduction of sound waves as electrical variations.

In the drawings, Fig. 1 is a circuit diagram indicating a telephone system embodying one form of the invention and comprising a central station and two substations of similar type connected thereto, and Figs. 2 and 3 indicate modified types of substations which may be substituted for the type of" substation shown in Fig. 1.

In Fig. 1, subscribers stations or substations 1 and 2 are connected to central station 3 by the two-conductor lines 4 and 5 respec-- tively. Lines 4 and 5 may be of consider able length, and are dashed in the drawing, to indicate that the central station may be The central station comprises a common battery or other D. C. source 6 and a repeating coil having inductively related windings 7 and 8. At substation 1 is a telephone transmitter 10 working into an amplifier 11 through a transformer 12, the amplifier in turn workiug into line 4 through a transformer 13 which preferably has a primary winding connected in series with condenser 14 across the anode and the cathode of the amplifier, a secondary winding connected in series with a switch 15, an impedance 16, and a con- 5, 1923. Serial No. 680,785.

denser 17 across the line 4. A telephone rein serial relation with condenser 14 across line 4 at station 1, this condenser and this bell being proportioned to respond to currents of ringing frequency sent to station 1 over line 4. It will be understood that signaling apparatus, ringing apparatus, and operators listening in devices of any suitable type (not shown) may be provided at the central station.

The transmitter 10 may be of the pushpull microphonic type, as indicated in the drawing, which permits of high modulating efiicieny and faithful reproduction of sound waves as electrical variations. The amplifier is preferably of the electron discharge type, as indicated in the drawing.

The ratio of the transformer 13 is preferably such that it approximately matches the impedances facing its primary winding and its secondary winding, so that eflicient and faithful amplification of the current delivered by a transmitter 10 and transformer 12 may be obtained. The plate-to-filament impedance of amplifier 11 will ordinarilybe high compared .to the impedance facing the secondary winding of transformer 13 and therefore the impedance of the transformer in the direction from its primary winding to its secondary winding, will ordinaril be made large in comparison to its impe ance in the other direction.

Since the amplifier 11 isa voltage operated device, the transformer 12 is preferconductor of line 4, back to source 6.

Normally, the weight of receiver 20 maintains receiver switch 15 open against its bias, and no current flows in transmitter 10 or amplifier 11. A subscriber at 1, for example,

wishing to talk with a subscriber at 2, removes receiver 20 from receiver switch 15, which thereupon closes, thus allowing D. C. to flow from source 6 through winding 7 the lower conductor of line 4, switch 15, conductor 27, the two sides of transmitter 10 and the two halves of the primary winding of transformer 12 in parallel, conductor 28, a retard coil 37, the filament of tube 11, leads 29 and 30, and the upper conductor of line 4, back to source 6. This current'energizes the filament of tube 11 and also renders the transmitter 10 operative. This current, flowing through the two halves of the primary windin of transformer 12 in opposite directions, of course produces no magnet izing effect in the transformer. I

On closing the switch 15, the subscriber at station 1 signals the operator at the central station, who connects station 1 with station 2, and then clears himself from the line, after, the subscriber at station 2 has removed receiver 20"from receiver switch 15'.

Upon the closure of switch 15, direct current from source 6 renders transmitter 10 operative and energizes the filament of amplifier 11' after the fashion in which transmitter 10 was rendered operative and the filament of amplifier '11 was energized upon the closure of switch 15.

When switch 15 closed, direct current. was also supplied to the plate circuit of tube 11, this current flowing from source 6, throu h winding 7, the lower conductor of line 4, the winding of bell 25, the primary winding of transformer 13,the plate filament resistance oftube 11, leads 29 and 30, and the u per 1111- ilarly, when switch 15 closed, space current from source 6 was supplied toamplifier 11.

llhen the system is in operation, condenser 17 prevents-the direct current forthe plate circuit of tube 11 from being shunted away from the plate-filament resistance of the tube through resistance 16 and the secondary winding of transformer 13. The magnets of bell 25 serve as a choke coil in the lead'for supplying direct current to. the plate of tube 11. As will be apparent from the drawing, the alternating components of the current in the output circuit of tube 11 HOW through the condenser 14 and primary of transformer 13.

Fig. 2 shows a modified form of substation which may be substituted for the substations in Fig. 1. In Fig. 2, a microphonic transmitter 10, of the unbalanced type is employed, instead of the balanced or pushpull type of transmitter-shown at 10 in Fig. 1. Elements of the substation shown in Fig. 2 are the same as those designated by like reasons reference characters, respectively, in Fi 1. in Fig. 2 the filament heating current flows between transmitter 10, and the filament through a retardation coil 37' and lead 28, a condenser 35 preventing flow of D. C. through the primary winding of transformer 12. Receiver 20 in Fig. 2 is connected in side tone relation to transmitter 10 and tube .11, whereas, aS noted above, the receiver 20 in Fig. 1 is connected in anti-side tone relation to the transmitter 10 and tube 11. Con- I tion, instead of the transmitter 10 of Fig. Y

1. In Fig. 3, an auto-transformer 131, is employed, instead of the transformer 13 of Fig. 1 and anti-side tone circuit, such as disclosed in F. W. McKown Patent.1,52l,4.02 of January 27, 1925, comprising a balanced receiver 20 is employed, instead of the antiside' tone circuit comprising receiver 20 employed in Fig.1. Elements 4, 11, 12, 14 and 25 have functions similar to those of the elements of Fig. 1 which are designated by the same reference characters respectively. In Fig. 3, a receiver switch 15 comprising upper and lower contacts, is employed, instead of the receiver switch,15 of Fig. 1. A point on the winding of auto-transformer 13, intermediate the ends of that winding is connected to a point on the winding of receiver 20 intermediate the ends of the latter winding by'means of a conductor 40; and the part of the receiver winding between the latter point and the upper contact of switch 15 embodies a resistance corresponding to the resistance 16 of Fig. 1. for balancing the impedance of line 4 which faces the substation of Fig. 3. In Fig. 3, the upper conductor of line 4.- is connected to the positive pole of source 6 (not shown) instead of to the negative pole as in Figs. 1 and 2; and the lower conductor of line 4 in Fig. 3' is connected to the negative pole of the source 6, instead of to the positive pole as in Figs. 1 and 2.

In the operation of the substation of Fig. 3, when switch 15 is closed, direct current flows from the upper conductor of line 4, through the windings of hell 25, a lead 42, the upper contact of switch 15,, the upper portion of the winding of receiver 20,, lead 40, the lower'poition of the winding of autotransformer 13,, and the filament of tube 11. to the lower conductor of line 4; and direct current also flows from the upper conductor of line 4, through lead it, the lower contact of switch 15 the lower portion of the winding of receiver 20,, lead 40, the lower poi-.- tion of the winding of the auto-transformer 13 and the filament of tube 11 to the lower conductor of line 4. These direct currents energize the filament of the tube 11, the latter current exerting the principal part of this energizing effect. Therefore, direct current for the plateto-filament circuit of the tube flows from the upper conductor of line 4, through the windings of hell 25, lead 42, upper contact of switch 15,, the upper portion of the winding of receiver 20,, lead 40, the upper portion of the winding of the auto-transformer 13 and the plate filament resistance of tube 11, to the lower conductor of line 4; and direct current for the plate-4 to-filament circuit of the tube also flows from the upper conductor of line 4, through lead 44, lower contact of switch 15,, the lower portion of the winding of receiver 20,, lead 40, the upper portion of the winding of auto transformer 13,, and the plate filament resistance of the tube, to the lower conductor of line 4. v

The general principles herein disclosed may be employed in many organizations varying from those illustrated without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. In combination, an element for amplifying electrical variations having an input circuit, an output circuit and an internal current path therebetween, a source of direct current remote from said element, a circuit for supplying direct current from said source to said path, and a transformer coupling said output circuit to the direct current supply circuit. i

2. in combination, a circuit comprising a telephone transmitter, an, electron discharge device fed from said transmitter and having an energizing circuit, a source of direct current remote from said transmitter and said device, means connecting said circuits to said source in parallel relation to each other, and a telephone receiver connected to said means in non-side tone relation to saidtransmitter and said device.

3. In combination, an electron discharge device having a space current circuit and having a cathode and a cathode heating circuit, said heating circuit including a telephone transmitter in series therein, a source of direct current, and means supplying said direct current from said source to said circuits in parallel with each other.

4, in a telephone system, an electric device comprising a sealed container having main lectrodes and an electrified conductor, a telephone transmitter and a telephone receiver at said device, a source of direct current remote from said device for rendering levice and said transmitter active, and means said device and actuated by movement of said receiver for bringing said source into operation.

5. In combination, a source of direct current, an amplifier and a telephone transmitter remote from said source, said transmitter feeding said amplifier, two conductors for transmitting voice current energy away from said amplifier and 'for supplying energy of said direct current from said source to said transmitter and to said amplifier, and a telephone receiver connected to said circuit at said transmitter in non-side tone relation to said transmitter and said amplifier.

6. In combination, a substation comprising a telephone transmitter and an electron discharge" amplifier having an anode, a cathode and a control electrode and having its cathode and its control electrode connected to said transmitter, a source of direct current remote from said substation, and a circuit for transmitting voice current energy away from said substation and for transmitting said direct current from said source to said anode, said cathode and said transmitter, said substation also comprising a telephone receiver connected to said second'circuit and in non-side tone relation to said transmitter.

7. A telephone system comprising a subscribers substation including an electrical wave amplifying element, a central station having a source .of direct current energy thereat, a pair of conductors connecting said subscribers substation and said central station, means for transferring electrical energy from said amplifyingelement to said conductors with voltage step-down, and means for conductively transferring electrical energy from said source of direct current energy and said conductors to said amplifying element. v

8. An electrical wave amplifier having output terminals, a source of direct current remote from said amplifier, a circuit for supplying direct current from said source to said amplifier, an impedance changing transformer connecting said circuit and the out put terminals of said amplifier, said transformer having a winding connected across said circuit, and means preventing said Winding from shunting'said direct current away from said amplifier.

9. In combination, an electrical wave amplifier, a calling bell at said amplifier, a

source of direct current remote from said amplifier, and partly common circuits for transmitting ringing current to the winding of said bell and for supplying direct current from said source to said amplifier and said winding in series, whereby said winding serves as a retardation coil for substantially reducin variataions in said direct current supplies to said ampliiier,

10 A telephone systei'ii including a subscribers station, and a central station having a source 'of direct current energy thereat, a pair of line wires connecting said subscribers' station and said central. station, a space discharge device at said subscribers station having cathode, anode and grid or control elements, a transmitter at said subscribers station, a connection from the positive pole of said source of direct current at said central station over one of said line Wires to the anode of said discharge device, said connection including the primary winding of a speech transformer, a connection from the negative pole of said source over the other of said line Wires to the cathode of said device, a circuit in bridge of said line wires including the secondary winding of said speech transformer and a stopping condenser, and means operatively relating said transmitter to the cathode and grid of said device.

'11. A telephone system according to claim 10 in which said means operatively relating said transmitter to the cathode and grid of said discharge device comprises a circuit in bridge of said line wires and'including in series relation said, transmitter, the primary winding of a speech transformer and a heating circuit for said cathode, the secondary winding of said transformed'being connected between said cathode and said grid.

12. In combination, a space discharge device, an electromagnetic receiver comprising a winding, a source of energy for said winding, means comprising two separate paths to supply the energy from said source to said winding, one of said paths including the plate circuit having an energizing coil, a. source ofplate current in circuit with the" receiver energizing coil, and an impedance in shunt to the plate circuit whereby current may flowfroin said source through the receiver energizing coil independently of the space current ath of said tube.

14:. In com in'ation, a space discharge deelectromagnetic element having a win ing for producing a steady field, and a circuit for establishing a path of steady current flow JOHN IV. FOLEY.

vice, a source of space current therefor am; 

